Friday, August 11, 2017

Is summer weather over for midwestern, northeastern US?

August 11,2017, 11:07:17AM,EDT

The recent spell of September-like temperatures has some people in
the midwestern and northeastern United States wondering if summer
weather is over for the year.

While there is some more cool
weather to go during August for parts of these regions, don't write off
90-degree Fahrenheit heat just yet.More coolness to come
Cool
air will linger into the third week of August across much of the
Northeast and Midwest due to a weather pattern that will stay put.
"During
the third week in August, a jet stream pattern will set up that
resembles the Greek letter omega across the northern U.S. and southern
Canada," according to AccuWeather Lead Long-Range Meteorologist Paul
Pastelok.

The jet stream is a high-speed river of air located at the level in the atmosphere where jets cruise.
The
omega block creates somewhat of an atmospheric traffic jam. More cool
air will jam into the Northeast. Waves of warm and cool air will flow
over the North Central states. The most persistent warmth is likely over
the northern High Plains.
"Essentially, this omega block will
keep big heat locked up in the Southwest for much of the third week of
August," Pastelok said.
The sun is still strong enough to cancel
out some of the cool air by day with highs in the lower 80s in the
Northeast and Midwest.
The nights, however, will tend to be cooler
and feel more like September. Temperatures will drop into the 60s
fairly often in the Ohio Valley and coastal Northeast. Temperatures can
dip into the 50s in the normally cool spots of the Upper Midwest,
northern New England and the central Appalachians.RELATED:US East Coast may experience close encounter with tropical system early next weekSevere storms to batter US High Plains with flooding through the weekendRepeated downpours may inundate southern US with 10 to 20 inches of rain over next few weeks
The omega block will evolve once locally heavy thunderstorms cycle eastward this weekend and an Atlantic tropical system, dubbed 99L, departs early next week.
"Another
aspect of the weather pattern will be to create much drier weather over
much of the Midwest and Northeast, when compared to the first part of
August," according to AccuWeather Meteorologist Dean DeVore.
The
dry flow may even shelter New England and part of the mid-Atlantic from
torrential downpours early next week, indirectly associated with an
offshore tropical system. Downpours are most likely to concentrate along
the southern Atlantic coast.August may finish warm
Predicting
the development and breakdown of omega blocks are challenging. However,
if the pattern goes according to schedule, the omega block will break
down during the last part of August.

"We expect more of a west to east
flow with the jet stream with a slight northward bulge over the Great
Lakes during the fourth week of August," Pastelok said.
This setup
should allow some warmth to build farther north over the North Central
states, and some of that warmth should reach the Northeast on occasion.
During
the last part of August, the pattern may evolve enough to allow days
with highs in the upper 80s to near 90 from much of the Midwest to the
Northeast. This includes areas around the upper Great Lakes and northern
New England.Warmth may linger into September
"Looking
farther ahead into September, temperatures are likely to average a few
degrees above normal for the month as a whole," Pastelok said.
"However, people need to keep in mind that average temperatures trend downward as the month progresses," he added.
For
example, in Chicago and New York City average temperatures drop by
about 10 degrees from the beginning to the end of the month. On Sept. 1,
the average high is 80 for both cities. On Sept. 30, the average high
is near 70 for both cities.